Differential



DIFFEENTIAL Filed Jan. s; 192s s sheets-sheet 1 N VEN TUR IFECraze/farai WITNESSES TTUR/VEYS June 21,1927. 1,632,787

l F. E. CRAWFORD DIFFERENTIAL I Filed Jan. s. 192s s sheets-sheet 2Wig). Q i

f will., fk -1 WIT/VESSES INVENTOR Afro/mns Jun 21, 1927. 1,632,787

F', E. CRAWFORD DIFFERENTIAL Filed Jan. 5. 1923 3 Sheets-Sheet. 3

w/mssfs WEA/10H Crawford. ww

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Patented June 2l, 1927.`

UNITED STATIr-.Se

.1,632,737 en-friiixrrY oFFiclf-L.

FRANK Emana CRAWFORD, .or Yorin NEBBASK@ DrrFEREfNTLe- IL- ApplicatQnled January 3, .19273. Serial No. 610,5046.

rIhis invention relates to improvements in differentials.

In differential gearing heretofore proposed.` complete differentiationis secured or is entirely prevented, there being no means providedwhereby differentiation may be only restricted to a predetermined ratio,with the result that, in the former, the power of the engine may bespent in transmitting motion to but onedriving wheel. while in rthelatter manually operable means are temporarily employed to entirelyprohibit differentiation thereby giving the effect of a solid axle.

The purpose of my invention is ,to provide a device which automaticallylimits the scope of differentiation to a` predetermined and necessaryratio.

The greatest amount of differentiation necessary under ordinaryconditions is that which allows of the yehicle turning `in the smallestcircle of which its steering apparatus permits. lf, during the turningof this smallest circle with a` given'car, the inner wheel makes threerevolutions ywhile the outer wheel makes five revolutions, then, forthis cui', the necessary ratio of 3 to is established. For convenienceof expression l will employ this ratio. In my present inyention means.are shown for allowing Ythis inaxiniun'i differentiation 'and yetprohibiting any. greater ratio, while at the saine time either wheel ofthe vehicle may act anywhere between the ratio of 3 to oV while theother is compensating from 5 to 3. Differentiation is thus permitted andyet` limited,

kso that. motion is at alll times provided to both wheels ofthe motorvehicle.

Other objects and advantages relating to details of construction,combination andarrangement of parts will hereinafter appear in thedetailed descriptionto follow.

The invention is illustrated byv way of example in the accompanyingdrawings,'in

`which z,.-

l"Figure lis a sectional view of a differental runit taken on the lineV1 1 of Figure 2.

Figure 2 is a. sectional view taken substantially on the lines 2 '2 ofFigiii'el.

Figure 3 is a. top plan View ofthe differential vunit when removed fromits housing. Figure 4 is a perspective View of compen eating orconnecting unit interposed between each axle shaft and associated end ofdit 'i ferential gear casing.

Figure is a detail kperspective vview of cross section.

the pawls used in connection with each compensat-ing unit controllingthe movements of the axle shafts.

Like reference numerals refer to like parts throughout the views yof thedrawings.

Referring lto thedrawings more particularly. H indicates generally adifferential housing which may be of any desired shape with Ya view thatthe same will accommodate the different units of the pres-ent differ-VThe housing has the H ential construction. two usual hub portions 1,0and is also provided witli a suitable bearing as at 1l whereby tosupport the rear end of the driveV shaft generally indicated at S. Thedrive' shaft S carries the usualpinion P which is in constant mesh withthe` ring gear G cai'- ri-ed upon the differential vgear casing C. Thedifferential gear casing C ymay be of sectionalV formation and supporttherein Vin the usual manner the pinions P1 and the gears G1. Each'gea1Gl" istv secured upon 'the inner end of an axle shaft S1 and has anextend-ed hub port-ion as at l2.'

The differential gear casing is provided at ,each end with an ,annularoffset, the. .portion 13 of which is preferably octagonall in A secondoffsetis also proi'ided upon cach end ofthe differential gear casing C,and the bottom. portion 'la of Awhich is circular and adapted to presenta bearing surface.

Inteiposed between each end of the dit` ferential gear casing C and theassociated inner' sidel of the housing H, is va gear 15 which is formedwith a hub extension 1h which is adapted to substantially abut theextended hub portion 1Q of t-he associated differential gear G1. Thegear lo, in each instance, is splinedupon the associated shaft S1. Uponeach end of the Vdifferential gear casing C there is'posit-ioned a gear:ring l?` said gear ring being adapted to be Seated upon the associatedoctagonal` shaped end portion 13 and thus vbe rigidly held against.

turning movement .with relation to the cas` ing C.

that may be termed a ring carrying unit and generally designated by therefer- .ence character R is vprovided for each shaft S1. Theconstruction ofthis ring carrying unit is specifically shownin` Figure 4of the drawings and as is seen in ,this figure comprises an yannularmember Or ring 18 .which is formed upon its outer Vperiphery with anannular offset 19 said'offset oc- Vcurring upon .the inner edge of thering.

Also upon the inner side of the ring there is provided a pair ofrecesses 20. Thering 18 is rigidly secured to a cog wheel 21, whichfunctions as a ratchet-wheel, said cog wheel being of greater diameterthan the ring V18, as shown. A pair of pinions 22 and 23 respectively,are positioned in each of the recesses 20, and each pair` `of pinionsbeing rotatably supported by a stub shaft 24. The pinions 22 and 28 arein each instance secured rigidly tothe associated` stub shaft 24, andtliestub shaft 24 hasits ends journaled i'espectively'in the cogV wheel21 and the ring`18. 'lheopening 25 of the ring 18 `is of such afdian'ieter that the ring `may be journaled by the annular offset portion14 upon the associated end of the casing C, while the opening 26 of thecog 'wheel 2l, is adapted to receive an annular proti'usion 27 formedupon the associated inner end of the housing H; The cog wheel 21 is inthis manner rotatably `supported by the housing H and the ring 18likewise supported by the `gear casing C." This is true with respecttoeach ring carrierunit R. V1When each ring carrier Vunit R is positioned`as illustrated in Figure 1 ofthe drawings, the pinions 22 are in meshwith the gear 15, while the pinions 23 'are in mesh with the gear ring17. y i

l/Vithin .the groove formed by offset 19 on the ring member 18 there ispositioned `an nternal ring gear 28, said ring gear being in mesh withthe pinions 22. About this internal ring gear there is positioned a'divided band 29 which has each of itsends lformed `with a lateralprojection 30 and said projections being connected by a bolt 81, the

bolt 31 being passed through suitable aligned Y openings in saidprojections and -o'f `the length shown. and interposed between this nutand the associated projection 30 is a coil spring 33. As is obviousthe`tension of the member 29 upon the internal ring gear 28 may be adjustedby manipulating the nut 32. Suitn able friction lining may be positionedupon the inner side of the band as indicated f at 34, Figure l.

Upon the outer .periphery of thevmember V29 there is secured a'metalstrip 35 which is formed adjacent each of its ends with a protrusion36and each protrusion presenting a point 37 and an inclined surface 38,said inclined surfaces 38 extending in opposite directions. For eachprotrusion 36 there is provided a pawl generally indicated bythereference character 39 and specifically shown in Figure 5v of thedrawings. Each of the pawls consist Vin `a shank portion40 whichterminates in'. a downwardly extending lip 41 whichV has its lower `endbevelled as at 42. The `shank portion 40 of each pawliis provided withan opening 48 adapted to receive the one end of astud 44. The studs Thisbolt carries a nut 82k 44 are in each-instance threadedginto theassociated end wall of tliehousing H, and each Vstud is provided with acollar 45 adapt-V ed to limit theinWardmOVement of the associated pawl.A leaf spring 46 is provided for each pair of pawls 89, said leaf springin each instance being rigidly supported at a point intermediate itsends as at 47 4from suitable means extending from the housing yH, andthe ends of said leaf spring being adapted to engage upon the opposingends ofthe associated pawls 3S) and depress said pawls downwardly.` Y lA slide bar 48 is extended through a suitable slot in the housing H andterminating the associated motor vehicle in such a inanner that upon thegear shifting lever being brought to a position for any of` the forwardmovements of the motor vehicle, the head 49 of the slide 48 will bepositioned as in Figure 2 of the drawings. It is of course apparent thatthis slide may be manually manipulated if so vdesired and not connectedwith the gear shifting lever. Then Vthe gear shifting lever of the motorvehicle is positioned for reverse drive, then the slide 48, toaccomplish the results of the present invention should be shifted sothat its head will be positioned beneath the rearmost pawl 39 and itsinclined surface52 engaging the ,rearmost pawl 39for lifting the same;It

should be further noted that two operating slides 48 must be provided.in order to oper atethe two sets of pawlsV 39, and the manner in whichthese slides function with respect to the pawls 39 will be ,clearlydescribedin the' description to follow.`

The operation ofthe present apparatus is y l' as follows: Assuming thatthe vehicle with which theV )resent differential isV cooperated isdriving in a straightand forwarddirection, then power is transmittedfrom the drive shaft S to the axle shafts S1 in equal'V ratio andintlieusual manner. While each `rear. wheel of the motor vehicle is turning`at the same rate of speed theratio of the gears 17 and 15 forrdrivingthe pinions 22 and28 is :such that the ring carrier unit, -in eachinstance, will rotate at a rate equal to that ofthe wheels and also thatof the differential gear casing. Now should either one "of the axleshafts S?, be reduced in speed to the ratio of 3, while the otherhasfin-V creased to the ratio of 5, then the ring carrier unitI7associated with the axle making the lesser number of revolutions willcome to a stop and should Vthe tendency' of the rear wheels be toincrease this ratio( of ldiffer-y entiation, then the tendency of thering carrier unit? R associated with the sha-ft axle making the lessernumber of revolutions will be to turn backward. Referring to Figure 2 itwill be seen, that the split ring 29 cannot rotate in a left handdirection, due to the fact, that its forward protrusion'36 engages theforward pawl carrying stud 44:. This is true with respect to each ringcarrying unit. The reariiiost pawl of each unit is elevated and restsupon the inclined surface 38 of the associated projection 36 and is soheld by the tension of the spring 46. Now `upon the ring carrierattempting to turn inthe opposite direction, the friction member 29 willbe carried therewith and will continue in such a movement until therearmost pawl 39 engages the teeth of the cog wheel 21 and brings thesame to a stop. Upon this occurring the gear casing C will transmit itsmotion through the pinionsv 22 and 23 to the gear lvwhich in turn willtransmit the motion tothe associated axle shaft S1 and thereby bringthis shaft to rotate withintlie proper rate of speed which representsthe lowest speed of the one axle shaft 'with respect to the other in thepresent differential construction.

Upon the axle shafts again returning to their normal differentiation,thatis, within the `ratio Vof 3 to 5, Ithe brake ri-iig 29 will returnto its original position as shown in Figure 2 and thus the ring vcarrierR will again function'in its original manner.

The description ,heretofore given relative vto the operation of oneringA carrier unitvis also true with relation to the other and thus itbecomes obvious that by this arrangement,

`the differentiation of the two axle shafts S1 may be held within theratio of 3 `to 5 as intended. It also may be herestat'ed that the ratiomaybe changed by'changing theconstruction'of the gears 15,17, 22 and 23.

In case that this lparticular rat'iogof dif fereiitiation is desiredwhen the vehicle `is moving Yin 4a rearward direction, then the levers48as heretofore stated'are moved so that theyengage with therearm'ostpawlsg39.

The operation `for maintaining this vdifferentiation upon Vrearwardmovement of the vehicle is the vsame as that heretofore described forforward movementofthe'vehicle" with the exception-that the -pawl's v39operate in an exact reverse manner.

ferential through breakagev of the drive shaft, or stops ofthe engine,or the like and was ascending a steep grade, the present invention wouldoperate to positively prevent-the motor vehicle from running backwards.This would be due to the fact that the pawl 39 `would come intoengagement with the ring` gear 21 and lock the same against tiirningmovement. The locking kof this ring gear .would in turn lock theassociated pinions' 22 and 23 and thus lock the spindles S1.'

.lVliile I have shown and described the prefeired forni of my invention,I wish it to be understood that I am aware of the fact, that theconstruction, combination and arrangement of parts may be changed bythoseV skilled in the art without departing from the spirit of theinvention, as indicated by the appended claims.

1What I claim is ll. A- differential unit including a rotativedifferential gear casing and a pair of spindles driveii'tliereby incombination, connecting means comprising a rotative vreducing gearcarrier and reducing gears rotatively mounted in said ycarriers betweeneach spinvvdle and said rotative differential gear casing whereby therotative-movement `of either spindle in one direction `may be maintainedvwithin a predetermined degree with respect l to the rotational speed ofsaid differential gear casing, means 'to lock said carriers againstreverse rotation, and meaiisoperable from a remote point to permitrotation of said carrier in said reverse direction and to locl; Vitagainst other rotation, whereby the connecting means between eachspindle'and :iti

differential -gear casing may be caused to operate for maintainingtherotative relation between said gear casing and spindles 'when saidspindles are r tated in the opposite direction. i

l l'fnconibination, a motor vehicle, a dif` -ferential unit thereforincluding a rotative differential gear casing and a pair of spinagainstreverse rotation, and means operable from a remote point to permitrotation of `said carrier in said reverse direction "and -to lock itagainst other rotation, wliereby` the connecting means between eachspindle "and said rotative differential gear casing may be adjusted tocause a like'rotational relation between said spindles and saidroftative differential gear casing upon Vany rearward movement 'of saidmotor vehicle.

3. In a differential unit including a rotative diffei'entialgearvcasing, a pair of spindles driven by said differential unit, a controlunit for eachV spindle consisting in a f gear fixed upon the gear casingof the differential unit, a gear fixed upon the spindle, a` carrierrotatable about said gears, connecting means between said carrier andthe gears wherebythe carrier will rotate in a certain direction as longas the spindle `maintains a predeterminedispeed of rotation withrelation to the gear casing, said connecting `means :being also adapted`to cause the Carrier to reverse its direction of rotationupontliexrotation of' the spindle falling below this` predetermineddegree, means whei'eby the carrier maybe held against reverse rotation,and power may be' transmitted yfrom the gear Acasing to said spindleduring the interval said carrier is held against reverse rotation.

4. In a differential unit including a rotai tive differential gearcasing, a pair of spindles driven by said unit, a control unit -for eachspindle consisting in agear fixed upon Vdle iii one direction as long asthe` speed of rotation of the spindle does not decrease beyond apredetermined degreewith respect to-the speed of the gear casing, andupon `this spindle decreasing iii speed a predetermined amount, saidpinions operating to rotate the carrier iii a reverse direction, meanswhereby said carrier may be held against reverse rotation and therebycausing the power to be transmitted.through said pinions and `gears fromthe gear casing to said spindle.

y 5; In a differential unit including a rotative differential gearcasing, a pair of spindles driven by said unit, acontrol unit for eachspindle consisting in a gear fixed Vupon the spindle, a gear fixed uponthe gear casing of the differential unit, a pair of pinions,A a carrieradapted to support said pinions for rotation about said gears and topermit one of said pinions to be in constant mesh withthe gear upon thegear easing and the other pinion in constant mesh with'the gear upon thespindle, said gear and pinions being` ofsuch a ratio that the same willrotate the, vcarrier about the spindle' in one direction aslong as thespeed of rotation of the spindle does not decrease beyond-a predeter-Vmined degree with respect tothe speed of the gear casing, and upon thisspindle `decreasingin speed a predetermined amount, said pinionsoperating to rotate the carrier in a reverse direction,andautomaticoper- Y ating means adapted to, lock the carrier againstreverse rotation. y v 6. In a differential unit including airotativedifferential gear "casing, a pair of spindles driven by said unit, acontrolunit `for each spindle consisting Vin, a gear fixed upon the`spindle, a gear fixed upon the gear casing `ofthe differential unit,l apair of pinions, acarrier adapted to support said lpinions `for.rotation about said gears and to permit one of said pinions to be inconstant `mesh `with the .gear upon thegear casing and the other pinionin constant mesh with vthe gear upon theV spindle,` said gear andpinions being` of such a ratio `that the saine "will rotatetlie carrierabout the .spindle in one direction as long as the speed of rotationoft-lie spindle does not decrease beyond a predetermined degree withArespect to the speed of the gearfcasing, and upon this spindledecreasing in speed a predetermined amount, said pinions operating torotate the carrier in a reverse direction, an internal ring gear in meshwith one of said pinions and adapted to permit said pinion to'trackthereon when said carrier `isrotated, and means` associated with said`internal ring gear whereby with the carrier tending to rotate intheopposite direction, the saine wil-l `be locked against this` movementand thereby Vcausing, the pinionsand 'gears to transmit power fromthegear casing to said spindle. i p y y Y y 7. In a dierential unitincluding a rotative differential gear casing, a pair of spindles drivenby @said Vunit,` a control unit Y. for l fioo` each spindle consistingin a gear fixed upon the spindle, a gear fixed upon the gear casing ofthe differential-unit, a pair of pinions, a carrier adapted to supportsaid Vpinions for rotation about said gears and to permit one of saidpinions to be in constant mesh with the gear upon the gear casing andthe other pinion in constant mesh with the gear upon the spindle, saidgear and pinions being of such aratio that the same will rotate thecarrier about the spindle in one direction as long'as the speed ofrotation ofi-the spindle does not decrease beyond a predetermined degreewith respect to the speed ofthe gear lcas1ng,and upon this spindledecreasing in speed a predetermined amount, Vsaid pinions operating torotate the carrier in a reverse directioman internal ring gear in meshwith one of said pinions and adapted to permit said pinion to trackthereon wliensaid carrieriis rotated, a frictionV bandV about saidinternal gear ring, means to limit-the-rotation of said friction bandinboth directions,

and meansoperable by the last named means `whereby upon the carrierrotatingina rever-se directioinvthe saine will be locked against thismovement and thereby causing the power to be transmitted from the gearcasing through said inter-meshing pinions and gears to said spindle.

8. In combination, a pair of spindles, a differential operativelyconnected with the spindles, Said differential including a rotativecasing, a rotative carrier, means to prevent reverse rotation thereof',and reduction gearing rotatively mounted in said carrier, between saidrotative casing and each spindle for positively driving the slowermoving spindle from the rotative casing at a rate of speed less thanthat of the casing when the ratio of differentiation reaches apredetermined degree.

9. In combination, a pair of spindles, a rotative differential gearcasing, differential gears in said casing, operatively connected withsaid spindles, gears on said casing and on said spindles and motiontransmission means comprising a rotative carrier, means to preventreverse rotation thereof, and reduc-ing gears rotatively mounted in saidcarrier between the gea-rs on said differential casing and on eachspindle andy independent of the mechanism of the differential' gears insaid casing, for positively driving the slower moving spindle from thedifferential gear casing when the ratio of differentiation reaches apredetermined degree.

10. In combination, a pair of spindles, a differential operativelyconnected with the spindles, said dierential including a i'otativecasing, a rotative carrier, means to prevent reverse rotation of saidcarrier, a set of gearing rotatively mounted in said carrier between therotative casing and each spindle for positively driving the slowermoving spindle from the rotative casing at a rate of speed less thanthat of the said casing when the ratio of dierentiation reaches apredetermined degree, each'set of gearing also serving to preventmovement of the spindle with which it is associated in a directionopposite to that to which said casing is moved.

l1. In combination, a housing, a pair of spindles rotatably mounted inthe housing, a differential within the housing and oper ativelyconnected with the spindles, said differential including a rotativecasing, a set of reduction gearing between the rotative casing and eachspindle, each' set of reduction gearing including a rotatable carrier, arotatable shaft mounted on the carrier, a pair of pinions fixed toSaidshaft, a gear fiXedly connected to the rotative casing and meshedwith one of said pinions, a gear fixedly connected to the `adjacentspindle .and meshed with the other pinion, and coopeiating mea-nsbetween the housing and the carrier for holding t-he carrier againstmovement in'a direction opposite to that of the direction of movement ofhe rotative casing.

12. `In combination, a pair of spindles, a

differential operatively connected with said spindlesand includingarotative casing, a set of'gearing between the rotative casing andl eachspindle, each set of gearing including a rotatable carrier, arotatableshaft mounted on the carrier, a pair of pinions fixed to saidshaft, a gear fixedly connected to the rotative casing and meshed withone ofvsaid pinions, a gear fixedly connected to the adjacent spindleand meshedwith the other pinion, and means forrholding the carrieragainstrotation when theratio of differentiation reaches a predetermineddegree.

13. In combination, a pair of spindles, a differential operativelyconnected'with said spindles, a rotative carrier, means to preventreverse rotation thereof and a separate set of normally inactive speedreduction gearing rotatively mounted on said carrier, `between thedifferential and each spindle, each set of' yspeed reduction gearingbeing independent of the mechanism of the differential. f

14. In combination, a pair of spindles, a differential including arotative gear case, operatively connected with said spindles, a

lrotifitive carrier, means to prevent reverse rotation of said carrier,and means, comprising gears rotatively mounted in saidv carrier, gearsmounted on said gear case vand gears mounted on said spindles, andindependent of the mechanism of said'differential for positivelydriving` the spindles when the ratio of differentiation reaches apredetermined degree. a

l5. In combinationwith a differential including a rotative differentialgear casing .and driven differential members, gears op`- erativelyyassociated with said casing and with said driven members, respectively,a pair of' rotative carriers, means to prevent reverse rotation of saidcarriers, reducing gears rotatively mounted in said carriers andoperatively associated with said first named gears, for positivelydriving one of said driven members from the reducing gears in one ofsaid carriers when the ratio of differentiation between said drivenmembers reaches a predetermined degree.

16. A differential unit including a rotatively mounted differential gearcasing, differential gears in said casing, rotatively mounted carriers,means to prevent reverse rotation of `said carriers, andreducing gearsrotativelly mounted in said carriers, .and spindles driven by saiddifferential gears, in combination with connecting means between saiddifferential and said reducing gears and vbetween said spindles and thereducinggears, whereby the speed of 'rotation at which said spindles aredriven will lll) be maintained within a predetermined ratio by saidreducing gears.

17. A differential unit including a rotatively driven differential gearcasing, a pair of spindles controlled thereby, and rotative carriers,reducing gears rotatively mounted in` said carriers, and means toprevent reverse rotation of said carriers, in combination, connectingmeans between each spindle and said gear casing, between said carriersand said casing and between said spindles and said reducing gears,whereby the rotative movement of either spindle in one direction may bemaintained less than and within a predetermined degree with respect tothe rotational speed of said differential gear casing, and meansoperable from a remote point whereby the connecting means between eachspindle and said differential gear casing and between each spindle andsaid carriers may be caused to operate for maintaining the rotativerelation between said casing, spindles and carrier when ro- Y tated inopposite direction.

18. In a differential unit including a rotatively mounted differentialgear casing, differential gears in said casing, a pair of spindlesdrivenby said gears, a control unit for each spindle consisting in a gearfixedupon said casing, a gear fixed upon the respective spindles, carriersrotative about said spindles, reducinggears rotatively mounted on saidcarriers, connecting means between said reducing gears and said casing,and between said reducing gears and said spindles, whereby thecarrierwill rotate in a certain direction as long las the spindles maintain apredetermined ratio of rotation, said connecting means being alsoadapted to force said carrier to reverse its direction of' rotation uponthe rotation Vof the spindles falling below said determined ratio, meanswhereby the carrier is held against reverse rotation,

whereby power may be transmit-ted from the gear casing to one of saidspindles during the interval said carrier is held against reverserotation.

19. A differential unit including a i'otatively mounted differentialgear casing, a pair of rotatively mounted carriers, reducing gearsrotatively mounted insaid carriers, and a pair of spindles, means toprevent reverse rotation of said carriers, in combinal tion withconnecting means between said spindles and said gear casing, connectingmeans between said spindles and said reducing gears,.and connectingmeans between said reducing gears Vand said casing, whereby the rotationof either spindle is maintained in the same direction within apredetermined degree of the rotation of said casingrduring any forwardmovementof said casing.V

20. A pair of spindles, a differential oper-` atively connected withsaid spindles, rotative carriers, gears rotatively mounted onv reverserotation, whereby when said gears act in certain relation saiddifferential functions and whensaid action in said relation ceases saidrotative carriers function to positively drive said spindles.

21. A driving device for a pair of spindles including gears on saidspindles, a rotative differential gear case, planetary gears in saidgear case arranged to drive the spindles to .permit va differentialmovement thereof, in

combination with additional gears on said spindles, rotative carriers,means to hold said carriers against reverse rotation,`gears on said gearcase and gears rotatively mounted. on said carriers connecting saidcarriers to said gear case and to said additional gears to positivelydrive saidV spindles when a determined differential ratio between saidspindles is obtained.

22. A driving device for a pair of spindles comprising a rotativedifferential gear case, gears rigidly mounted on said gear case, gearsrigidly mounted onv said spindles, a rotative carrier, reducing gearpinions rotatably mounted on said carrier and connecting said gears onsaid gear case and said'gears on said spindles, means to hold saidcarrier against rotation in a determined direction, for positivelydriving the said spindles upon 4a limited amount of' differentialmovement between said spindles being attained.

v23. In combination, a pair of spindles, a rotative differential gearcasing,` rotativie gear carriers, differential gears in said casingoperatively connected with said spindles, gears rigidly mounted on saidcasing and additional gears rigidly mounted on said spindles, means topreventreverse rotation of said carriers, reducing gears rotativelymounted in said carriers between said gears on said casing and saidadditional gearson said spindles, all arranged to positively drive theslower rotating one of said spin dles from one of said gears on saidcasing when the ratio ot differentiation between the spindles reaches apredetermined degree.

24. In combination, a pair of spindles, a rotative differential gearcase, differential gears in said case, operatively connected with saidspindles, gears mounted on said case and gears mounted on said spindles,motion transmission means between said gears on said case and on saidspindles, and means to prevent reverse ,rotation of said transmissionmeans, whereby said case is the source of power for positively drivingthe slower rotating one of said spindles when the ratio kofdifferentiation between the spindles reaches a

